In a wide range of fields, such as automotive, electrical/electronic, and the like, engineering plastics, in which constituent materials of components that had previously been made of metal materials, are replaced by resin materials and have contributed to lighter weight and lower cost of the components. However, since components made of resin materials alone as the constituent material have insufficient strength and rigidity at high temperatures, inadequate resistance to specific chemical substances, and the like, replacement of metal with resin materials is reaching a limit. Moreover, it has been attempted to improve surface texture, corrosion preventive function, and the like in components made of metal materials alone, through compositing or through multi-layering with resin materials. However, these attempts may bring about deficient strength of the component as a whole due to poor bonding of metal and resin, or diminished functionality of the component due to infiltration or accumulation of liquid in the joined portions of the metal and the resin in cases of components that come into contact with liquids.
In these circumstances, there exists a need for a technique for secure bonding of metals and resins, and a number of methods have been proposed. For example, Patent Document 1 discloses a composite body obtained by contact-bonding a thermoplastic resin composition (A) containing a thermoplastic resin and an inorganic filler that increases the crystallization temperature of the thermoplastic resin by 3° C. or more, and a surface-treated metal (B).
Further, Patent Documents 2 to 4 disclose and propose techniques of performing specific treatments on the metal so as to bond the resin and the metal with each other.